Flow meters may measure the rate of flow of a fluid in a pipe or other pathway. The fluid may be, for example, a gas or a liquid, and may be compressible or incompressible. One type of flow meter is a vortex flow meter which measures parameters including, for example, flow rate based on the principle of vortex shedding. Vortex shedding refers to a natural process in which a fluid passing a bluff body (sometimes referred to as a shedder) causes a boundary layer of slowly moving fluid to be formed along the surface of the bluff body. A low pressure area is created behind the bluff body and causes the boundary layer to roll up, which generates vortices in succession on opposite sides of the bluff body. The vortices induce pressure variations that may be sensed by a pressure sensor. The vortex-shedding pressure variations have a frequency that is related to the flow rate. Accordingly, by measuring the frequency of the pressure variations, the flow rate may be determined.
Vortex flow meters provide vortex frequency data that can be used in conjunction with flow calibration factors determine the velocity and volumetric flow rate of the fluid passing through the meter. With inputted fluid density values, the mass flow rate can also be computed. These measurements, and others, can be transmitted to a control room or other receiver over a communication line, such as, for example, a standard two-wire 4-20 milliamp (“mA”) transmission line.
In some applications (e.g., in the oil and gas, mining, chemical, and waste industries), the fluid flow monitored by a vortex flowmeter may sometimes include sand, minerals, or other abrasive particles. Over time, abrasive fluid flow can erode the bluff body, the inner the surface of the conduit containing the bluff body, and/or other features of a vortex flowmeter. The calibration factors used in the conversion of vortex shedding frequency to volumetric flow rate are based on the initial physical configuration of the bluff body and other parts of the vortex flowmeter. Erosion of these structures by abrasive fluids introduces error in the flowmeter. Thus, abrasive fluids can reduce the life of a vortex flowmeter.
The present inventors have developed systems and methods, described in detail below, that improve the ability operate a vortex flow meter with fluids that contain abrasive particles.